Pirates have hijacked an oil tanker with eight Sri Lankan crew on board, Somali authorities said last week, the first time a commercial ship has been seized in the region since 2012.

Security forces have been sent to free the Aris 13, a regional police official said late on Tuesday.

"We are determined to rescue the ship and its crew. Our forces have set off to Alula. It is our duty to rescue ships hijacked by pirates and we shall rescue it," Abdirahman Mohamud Hassan, director general of Puntlandís marine police forces, told Reuters by phone.

Puntland is a semi-autonomous northern region of Somalia. Alula is a port town there where pirates have taken the tanker.

Experts said the ship was an easy target and ship owners were becoming lax after a long period of calm.